1. Field of the Invention
The present invention is broadly concerned with biodegradable and edible packaging composites or containers comprising self-sustaining bodies and formed from a mixture comprising a non-petroleum based, biodegradable adhesive and a quantity of fiber. More particularly, the containers comprise a fiber derived from a fiber source selected from the group consisting of straw (e.g., wheat, rice, barley), corn stalks, sorghum stalks, soybean hulls, peanut hulls or any other fibers derived from grain milling by-products), and mixtures thereof. The adhesive can be protein-based or starch-based, and is preferably formed by modifying a protein, starch, or protein-rich flour with a modifier comprising alkaline materials and/or modifiers having particular functional groups. The resulting mixture has a low moisture content and is molded at high temperatures and pressures to yield a final container having high compressive strengths.
2. Description of the Prior Art
Livestock gel blocks are currently utilized for supplementing the diets of sheep, horses, and cattle in both feedlot and open grazing conditions. The blocks are formed of gels which are flowable at a temperature of about 80xc2x0 C. These gels are poured into a container and become rigid upon cooling. The gel blocks have xe2x80x9ccold flow propertiesxe2x80x9d meaning that, although they appear to be a solid, the blocks will not retain their shape when subjected to stress (such as from the weight of other blocks or gravity). As a result, the gel blocks are not free-standing and must be in a container at all times. The gels turn into a thick syrup upon absorbing moisture from the air. This syrup is then consumed by the livestock.
Currently available containers for use with gel blocks include half steel drums, plastic tubs, and paper or cardboard containers. Each of these containers has undesirable properties. For example, the steel drums must be either thrown away or recycled after use. Recycling is generally preferred in order to minimize the quantity of waste in landfills and other disposal sites. However, recycling involves additional labor and expense as the drums must be collected and transported back to the feed manufacturer and then reconditioned (i.e., reshaped, cleaned, and sterilized) by the manufacturer before reusing the drum. Likewise, plastic tubs can be discarded or recycled but must undergo the same labor and expense involved in recycling steel drums. Furthermore, the plastic tubs result in the generation of plastic waste which presents a disposal problem for the consumer as well as a liability problem for the manufacturer.
Paper and cardboard containers have been attempted commercially as an alternative to plastic or steel. However, paper and cardboard containers do not perform adequately. One problem with paper and cardboard containers is that they are permeable to moisture at room conditions, thus allowing moisture to contact the gel. This causes the gel to turn into a syrup prematurely which then seeps through the container, making the products difficult to ship and store. Furthermore, these paper and cardboard containers do not easily biodegrade, leaving waste at the feeding site. Finally, the livestock may consume portions of these paper or cardboard containers, presenting a possible danger to the livestock if the paper or card-board is not processed following FDA standards.
U.S. Pat. No. 5,160,368 to Begovich discloses a biodegradable package for fast food comprising a body which is molded from a composition consisting essentially of an admixture of biodegradable natural materials comprising low-protein flour (i.e., about 10-15% by weight protein in the flour) or meal from edible gramineous plants (e.g., corn or sorghum), crushed hay of gramineous plants (e.g., wheat, sorghum, corn, or corncob leaves), apreservative, and aplasticizing agent. However, the ""368 package has a high moisture content prior to molding (about 50% by weight moisture), thus resulting in a container that often cracks when molded at the high temperatures and pressures necessary to obtain a strong container. Furthermore, the ""368 patent fails to use a strong adhesive which results in a package having inadequate mechanical properties for use in packaging of livestock feed gel blocks (which often weigh 250 lbs. each) and other applications which require a strong container.
There is a need for biodegradable and edible packaging containers which do not contain cracks or other defects and which have strong mechanical properties, allowing the container to be subjected to stress with little risk of failing.
The instant invention meets this need by providing biodegradable and edible composites having high compressive strengths. Broadly, the composites are in the form of a self-sustaining body formed from a mixture comprising a non-petroleum based, biodegradable adhesive and a quantity of fiber. These composites can be used as containers for livestock gel blocks as well as other applications such as flower and plant containers.
In more detail, the fiber utilized in the inventive composites is derived from a fiber source selected from the group consisting of straw (including wheat, rice, and barley), corn stalks, sorghum stalks, soybean hulls, peanut hulls, and mixtures thereof.
While most non-petroleum based, biodegradable adhesives which are capable of forming the high strength composites of the invention are suitable, it is preferred that the adhesive be formed by modifying a starch (e.g., cereal starch and legume starch), protein, protein-rich flour (i.e., soy flour or other flour having at least about 25% by weight protein, and preferably at least about 40% by weight protein), or mixtures thereof with a modifier selected from the group consisting of:
(1) alkaline materials (such as NaOH);
(2) saturated and unsaturated alkali metal C8-C22 (and preferably C10-C18) sulfate and sulfonate salts;
(3) compounds having the formula I: 
xe2x80x83wherein each R is individually selected from the group consisting of H and C1-C4 saturated and unsaturated groups, and X is selected from the group consisting of O, NH, and S; and
(4) mixture of (1), (2), and (3).
The C1-C4 saturated and unsaturated groups refer to alkyl groups (both straight and branched chain) and unsaturated refers to alkenyl and alkynyl groups (both straight and branched chain). Preferred compounds having the formula I are urea and guanidine hydrochloride. When urea is the modifier, the protein, starch, or protein-rich flour is preferably essentially free of urease, having less than about 10 activity units of urease. Alternately, a urease inhibitor can be added to the protein, starch, or protein-rich flour.
Saturated alkali metal C8-C22 sulfate and sulfonate salts include all alkali metal alkyl (such as octyl and dodecyl) C8-C22 sulfate and sulfonate salts. Unsaturated alkali metal C8-C22 sulfate and sulfonate salts include all alkali metal alkenyl (such as decenyl and octadecenyl) C8-C22 sulfate and sulfonate salts and all alkali metal alkynyl (such as octynyl and tetradecynyl) C8-C22 sulfate and sulfonate salts. Two particularly preferred modifiers in this class are sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS).
The adhesives are prepared by simply forming an aqueous slurry or dispersion of modifier and starch, protein, or protein-rich flour. This modifier slurry is mixed for about 1-400 minutes at a temperature of from about 15-70xc2x0 C. Preferably, the forming and mixing of the dispersion takes place under ambient temperature and pressure conditions.
The resulting adhesive is then mixed with a quantity of fiber. Preferably the particle size of the fiber is such that less than about 10% of the particles have a particle size of less than about 678 xcexcm. The fiber and non-petroleum based adhesive should be utilized in appropriate quantities so that the mixture and final composite or container comprises from about 5-20% by weight adhesive solids (i.e., all solid components in the adhesive on a dry basis), and preferably from about 10-16.7% by weight adhesive solids, based upon the total weight of the mixture or final composite taken as 100% by weight. The mixture and final composite or container preferably comprises at least about 70% by weight fiber solids, and preferably from about 80-95% by weight fiber solids, based upon the total weight of the mixture or final composite taken as 100% by weight. The ratio of fiber solids to adhesive solids should be from about 2.5:1 to about 20:1, preferably from about 4:1 to about 15:1, and more preferably from about 5:1 to about 9:1.
The formed mixture is then dried to a moisture content of less than about 20% by weight, preferably from about 5-15% by weight, and more preferably about 11-13% by weight, based upon the total weight of the mixture taken as 100% by weight. It is preferred that no preservatives be added to this mixture so that the final composite is essentially free of preservatives. In one embodiment, the mixture consists essentially of a non-petroleum based, biodegradable adhesive and a quantity of fiber.
When a protein or protein-rich flour is modified to form the biodegradable adhesives utilized in preparing the composites of the invention, the protein or protein-rich flour should be included in sufficient quantities so that the concentration of protein in the mixture (i.e., the fiber mixed with the aqueous dispersion after drying) is at least about 5% by weight, preferably at least about 7% by weight, and more preferably at least about 9% by weight, based upon the total weight of the mixture taken as 100% by weight. Suitable proteins for forming the adhesives include those selected from the group consisting of soybean protein, wheat protein, corn protein, sorghum protein, and mixtures thereof
The dried mixture is then molded into a package having the preferred shape for the particular application. Molding is carried out by subjecting the shaped mixture to molding temperatures of from about 150-500xc2x0 F., and preferably from about 200-350xc2x0 F., and molding pressures of from about 150-600 psi, and preferably from about 220-450 psi. The molding process should be carried out for a time period of from about 1-20 minutes, and preferably from about 3-8 minutes. Molding can be carried out on any conventional molding presses known in the art, so long as the press is able to accommodate the foregoing temperature and pressure conditions. Furthermore, the mixture can be molded into virtually any shape, depending on the particular application. Preferred shapes for use in livestock feed supplements include box-shaped and half-barrel-shaped containers.
The final, molded composite or container should have a moisture content of less than about 10% by weight, and preferably less than about 5% by weight, based upon the total weight of the composite or container taken as 100% by weight. The final composite or container should have an ASTM D1037-93 compressive strength of at least about 5 MPa, preferably at least about 8 MPa, and more preferably at least about 10 MPa. Furthermore, the biodegradable composite or container should be essentially decomposable within about 1 year of being placed in the environment, depending upon its exposure to moisture and/or light. Finally, a moisture barrier (such as an FDA food grade wax) can be applied to the surfaces of the formed composite so as to minimize moisture absorption by the composite.